If i install new mac os do i have to delete the old os

#If i install new mac os do i have to delete the old os pro#

Once you plug it in then wait for it to get recognised you should see a message suck as 'USBHUB' like that once you see that type mkdir /usb then find the disk identifier of your pen drive by typing ls -la /dev/disk* you will find listings such as disk1 or disk1s1 your pen drive might be last disk listing. But I do still recommend taking a backup by booting into recovery and click Utilities in the upper menu bar and then select terminal then type csrutil disable then type reboot then when your Mac boots up and when you hear the chime hold CMD+S then wait until the plain text is done loading then type mount -uw / then grab a pen drive to plug in to your Mac and take a backup of your Mac. Reinatalling the os alone does not erase data. Again, the corruption might make this impossible. Otherwise, find a friend's Mac, and follow these Apple instructions to set your Mac in 'target disk mode' and allow the other Mac to access your files to copy them off. I recommend you review the step by step guides at to see if you are brave enough. Newer Macbook/Macbook Pros and iMacs make it much more difficult, as their SSDs are not removable or very difficult to remove.

#If i install new mac os do i have to delete the old os pro#

An older Macbook or Macbook Pro likely has a hard drive that is removable, allowing you to connect it externally using an enclosure or cable. To gain access to the disk depends on what model Mac you have. I will take this time to remind you that the time for backup is BEFORE you have an issue, so hopefully you have a Time Machine backup or Carbon Copy Cloner disk around. However, if there is a corruption issue, your data may be corrupted as well, its really hard to tell. If you have any problem please do comment below.Reinstalling macOS from the recovery menu does not erase your data. Trash and all the contents of your pen drive then type rsync -aH -exclude= ~/Library ~ /usb then it might take some time to take backup of your pen drive depending on the size of your home directory after it has completed type shutdown -h now. You might see some few lines such as kext like that if your disk was successfully mounted to make sure type ls -la /usb you should see. Then type mount -t msdos /dev/diskXs1 /usb (Note: X will be your disk identifier and if the file system o your pen drive is hfs or so make sure you replac msdos but if your pen drive is Fat or exfat don't change it. Once find that you might see disk3s1 or disk4s1.

Reinstalling macOS from the recovery menu does not erase your data.